Diabetic retinopathy (DR) and other forms of retinal ischemia are a leading cause of blindness in working age adults. There is a need to identify the mechanisms that control the transition from angiogenesis to fibrosis in these conditions. This would be a first step towards new therapies to address progressive vascular endothelial damage that ultimately leads to pre-retinal fibrosis and traction detachment with poor visual and anatomic outcomes. To address this gap in our knowledge, we have designed a series of experiments that build logically on our preliminary data, which shows evidence for endothelin-1 (ET-1) involvement in fibrovascular human surgical membranes. We hypothesize that dysregulated endothelial ET-1 is particularly important in the pathogenesis of ischemia-induced retinopathy and its complications. To examine this hypothesis, we will study animal models that span the entire spectrum of retinal ischemia, including streptozotocin (STZ)-induced diabetes and models of developmental ischemia- the oxygen induced retinopathy (OIR, to replicate angiogenesis in ischemia) and the limited hyperoxia-induced proliferative retinopathy (l-HIPR), which replicates the angiofibrotic end-stages of severe ischemia. We will use these models to test the hypothesis that dysregulation of vascular endothelial cell-derived ET-1 is critically involved in the promotion of vascular pathology, using an inducible, targeted vascular endothelial ET-1 knockout transgenic mouse (ET-1Eko). In aim 1, we subject this ET-1Eko mouse to the STZ-induced diabetes and the developmental models of ischemia to study the role of endothelial ET-1 dysregulation in angiogenesis and fibrosis. In aim 2, we will cross the ET-1Eko with a transgenic reporter mouse model to focus on the endothelial- to-mesenchymal transition in the retinal vessels and the surrounding pericytes, glia and neurons. Finally, in aim 3, we will focus on developing pharmacologic interventions geared towards ET-1 receptors to improve retinal pathology in models of DR, ischemia- induced angiogenesis and fibrosis (OIR and l-HIPR), as a first step towards translating our findings to the bedside. The mechanistic experiments proposed herein will capitalize on the interdisciplinary expertise of the clinician- scientist PI and her collaborators. Dr. Fawzi is a clinician-scientist retina surgeon with special expertise in non- invasive retinal imaging, animal models of ischemia and retinal vascular diseases. Her co-investigator, Dr. Schnaper is a clinician-scientist, pediatric nephrologist, who is a world expert in fibrogenic signaling. Finally, the group also capitalizes on novel imaging technologies in Dr. Zhang?s lab at Northwestern University, another collaborator.